Samara wings or blades for aircraft dispensed payloads such as cargo, supplies, munitions, and the like have previously been proposed. See U.S. Pat. Nos. 4,635,553; 4,583,703; 4,756,253; 5,067,410; 6,834,593; and 3,273,834 all incorporated herein by this reference. Once deployed, the wing spins (autorotates) much like a maple seed slowing the downward velocity of the payload attached to the wing. Steerable samara wings have also been proposed. See The Guided Samara: Design and Development of a Controllable Single-Bladed Autorotating Vehicle, Andreas Kellas, MIT Thesis, August 2007.
It is desirable in many air drop operations to have the payload quickly drop until at a lower elevation and a closer distance to the ground and only then slow the payload to a lower velocity for a softer landing. Also, winds aloft can adversely affect the accuracy of the desired drop point when the samara wing begins autorotating at high altitudes.
For most wing designs, the desire is to have a large amount of lift and a small amount of drag. The samara wing is no exception. The ratio of lift to drag is known as the wing efficiency. High efficiency is achieved by having some camber in the wing cross-section (the airfoil section.) Positive camber means the upper surface is more convex and the lower surface is either less convex, or flat, or even concave. This design creates a nose-down pitching moment.
It is difficult to design a single wing that has both pitch stability and pitch trim. The problem of designing a samara is very similar to the problem of designing a flying wing. The usual requirement for stability is to put the center of mass ahead of the aerodynamic center. This results in a nose-down moment. Something must be done to balance this moment. One solution is to use an airfoil section with upward curvature at the trailing edge, also known as a reflex trailing edge. Another solution that is used with flying wings is to have wing sweep and have the tips of the wings generate a down force. The term “wing sweep” means the left and right wings are swept relative to each other. Since a samara has only one wing, it is not clear what is meant by sweep.
A second problem could be called “control ambiguity.” The conventional way to increase the lift on a wing is to have a flap at the trailing edge that deflects downward. However, the lift will only increase if the angle of attack of the main part (the unflapped part) of the wing remains fixed. Since the samara is a single wing with very little pitch stability, were a flap deflected downward, the angle of attack of the main wing would decrease. The net result is ambiguous—the lift will increase if the flap effect is larger, or it may decrease if the angle of attack effect predominates.